1. Field of the Invention
The present invention relates to a coordinates input device, and more particularly to a coordinates input device which detects vibration input by a vibration pen by a plurality of sensors arranged on a vibration transmission plate to detect coordinates of the vibration pen on the vibration transmission plate.
2. Related Background Art
Conventional coordinates input device using various types of input pens and tablets for inputting hand-written characters or pattern into a processor such as a computer has been known. The image information of characters or pattern input by such an input device is output by a display such as a CRT display or a recorder such as a printer.
The coordinates detection of the tablet in such a system uses one of the following methods.
(1) A change in resistance of a sheet material arranged to face a resistive film is detected.
(2) An electromagnetic or electrostatic induction of a conductive sheet arranged to face a coil (an inductor) is detected.
(3) An ultrasonic vibration transmitted from an input pen to a tablet is detected.
In the methods (1) and (2) above, since the resistive film and the conductive film are used, it is difficult to provide a transparent tablet. On the other hand, in the method (3) above, the tablet may be made of transparent material such as acryl plate or glass plate. Accordingly, the input tablet may be overlaid on a liquid crystal display so that it may be used as if an operator writes a pattern on a paper. Thus, an information input/output device having a high operability is provided.
However, in the method which uses the ultrasonic vibration, the transmission of the vibration is impeded by a crack or obstacle on the vibration transmission plate of the tablet, and a detection precision is lowered.
It has been proposed to vibrate the vibration transmission plate of the tablet by using a plane wave of an elastic wave to reduce an affect by the crack or obstacle on the vibration transmission wave. However, in this method, since a surface wave component of the vibration affects to a detection waveform of the vibration sensor depending on an operation condition such as a vibration pen pressure or inclination, high precision coordinates input is not attained.